Add git authentication to support the private repo case

[Mazgis47]

Example usage:
bashbrew --library mylibrary --git-username MyGithubUser --git-password ghp_123456789 --debug --cache /tmp/bashbrew_cache --namespace docker-images.mycompany.com/myalpine build --all --pull always

[tianon]

Thanks for the contribution!

I think rather than adding explicit (manual) support for HTTP authentication to all our Git calls, I'd rather find out / figure out whether go-git supports https://git-scm.com/docs/gitcredentials properly so we can avoid having to specify this everywhere (especially since it's a feature we won't be using, so it won't be getting very much testing and we'll be likely to remove it if it ever has issues or requires changes).

[Mazgis47]

Thanks for the contribution!

I think rather than adding explicit (manual) support for HTTP authentication to all our Git calls, I'd rather find out / figure out whether go-git supports https://git-scm.com/docs/gitcredentials properly so we can avoid having to specify this everywhere (especially since it's a feature we won't be using, so it won't be getting very much testing and we'll be likely to remove it if it ever has issues or requires changes).

If I correctly understand they have an open issue on that src-d/go-git#1101 so it is a blocker/dependency to use go-git. There is an example provided but that is not a part of the go-git.

[yosifkit]

It looks like someone is currently working on adding git credentials support: go-git/go-git#490. So, we should wait until that is available.

(also, we shouldn't be pulling in any dependencies from src-d/go-git since it is an abandoned and archived repo and development has moved to go-git/go-git)